Stable microwave and millimeter wave signal sources fabricated via microstrip or planar circuit techniques on substrates are well known and are typically in the form of fixed frequency oscillators. One type of such oscillator comprises what is known as a dielectric resonator oscillator, an example of which is disclosed in, "A Highly Stable 36 GHz GaAs FET DRO with Phase Lock Capability," Microwave Journal, July 1989, by Khanna et al. This type of resonator oscillator uses a dielectric resonator to control the frequency of an oscillator by either a frequency "stabilized" DRO or as a frequency "stable" DRO. Khanna et al page 117.
Another type of oscillator is the ring resonator oscillator which exhibits not only relatively good frequency stability, but is simple in its circuit configuration. Moreover, transistor ring resonator oscillators integrate readily into miniature and microminiature integrated circuit technology where gallium arsenide (GaAs) field effect transistors (FET) are typically used. The details of a microstrip ring resonator oscillator are generally shown and disclosed in U.S. Pat. No. 4,185,252, entitled, "Microstrip Open Ring Resonator Oscillator", and issued to Gerlach on Jan. 22, 1980, which is incorporated herein by reference.
Both dielectric resonators and ring resonators work in a similar manner (the dielectric resonator may be substituted for the ring resonator). However, dielectric resonators are difficult to fabricate because a very small change in the position of the dielectric resonator can cause a large change in coupling resulting in a large frequency shift. Therefore, positioning the dielectric resonator is a labor intensive procedure. In contrast, ring resonators are processed directly on the circuit and need no extra time to position. The present invention is an adaptation of a ring resonator oscillator.